1. Field of the Invention
The present invention relates to a system for cooling an EGR (exhaust gas recirculation) gas and lubrication oil with engine cooling water.
2. Description of the Related Art
Systems for cooling an EGR gas with engine cooling water are known in the art. By cooling the EGR gas, the gas density is raised and EGR efficiency is improved. This type of conventional systems is called an EGR cooler, and one example thereof is disclosed in Japanese Patent Application, Laid Open Publication No. 10-169514 and illustrated in FIG. 8 of the accompanying drawings.
The EGR cooler 70 includes a generally cylindrical casing 72 extending between an exhaust gas line of an engine (exhaust manifold) and an intake air line (intake manifold). The casing 72 is divided into three chambers, namely, a gas inlet chamber 74, cooling water chamber 76 and gas outlet chamber 78, by two partition walls 80. A plurality of heat exchange pipes 82 extend in the cooling water chamber 78 and span the partition walls 80. The cooling water chamber 76 has a cooling water inlet 84 for introducing part of water, which is primarily used for cooling an engine, into the cooling water chamber. The cooling water chamber 76 also has a cooling water outlet 86 for discharging the water therefrom. An air ventilation 88 is further provided on the cooling water chamber 76 for allowing air, which is generated from the heated water, to escape from the cooling water chamber 76.
When the exhaust gas (high temperature gas) discharged from the exhaust manifold is partly recirculated to the intake manifold by an EGR line, that exhaust gas flows in the heat exchange pipes 82 and is cooled by the cooling water flowing in the cooling water chamber 76. This raises gas density of the exhaust gas and in turn EGR efficiency.
The EGR cooler 70 should be located between the exhaust and intake manifolds, but there is a cylinder head near the manifolds. Thus, only a limited space is available for the EGR cooler 70. Further, an engine hood and other structures associated with a vehicle body also exist in this area. In actuality, therefore, it is sometimes difficult to install the EGR cooler 70.
Moreover, since the cooling water is taken from the engine, introduced into the EGR cooler 70 and returned to the engine again, water pipes are required to connect the engine to the water inlet 84 and the water outlet 86 to the engine and at least one air pipe is needed for the air outlet 88. These pipes are subjected to vibrations when the engine is running and vehicle is cruising, and may have crack. To avoid it, the pipes must be firmly secured onto the engine with brackets and the like.
In addition, the EGR cooler 70 is completely independent from an oil cooler for cooling an engine lubrication oil, if any, so that it is not possible for the EGR gas to heat the lubrication oil (engine oil) in the oil cooler. Viscosity of the engine oil is generally low at low temperature starting.
Japanese Patent Application Laid-Open Publication No. 10-2256 discloses an EGR gas cooler using engine cooling water, and 7-42628 discloses an EGR gas cooler attached to a lateral wall of a cylinder block.
An object of the present invention is to overcome the above described problems.
Specifically, one object of the present invention is to provide a compact arrangement for cooling an EGR gas.
Another object of the present invention is to provide an EGR gas cooling system which is resistive to vibrations.
Still anther object of the present invention is to provide an EGR cooling arrangement which can also heat a lubrication oil when the lubrication oil temperature (or engine temperature) is low.
From another point of view, one object of the present invention is to provide an arrangement for cooling an EGR gas and lubrication oil, which is compact, does not vibrate and can heat the lubrication oil while cooling the EGR gas.
According to one aspect of the present invention, there is provided a system for cooling EGR gas and oil including a housing directly attached to a cylinder block such that engine cooling water flows in the housing, an EGR gas heat exchanger placed in the housing such that EGR gas flows in the EGR gas heat exchanger, and an oil heat exchanger placed in the housing adjacent to the EGR gas heat exchanger such that a lubrication oil flows in the oil heat exchanger. Since the two heat exchangers are located adjacent to each other and immersed in the cooling water in the housing, no piping is needed for introducing the cooling water into the housing. This improves resistance to vibration and reduces installation space. Further, since the two heat exchangers are closely located, heat of the high temperature EGR gas flowing in the EGR heat exchanger is transferred to the low temperature lubrication oil flowing in the oil heat exchanger via the cooling water when the engine is started under a cold condition. Thus, the lubrication oil is heated and its viscosity is lowered. This is particularly advantageous at the cold starting of the engine because the engine oil has high viscosity and the heated oil assists easier start up of the engine and reduces oil pump friction.
An opening may be formed in a lateral wall of the cylinder block such that part of a water jacket is exposed, and the housing (or a cover) covers the opening watertight such that the engine cooling water flows into the cover from the water jacket and vice versa. The EGR gas heat exchanger and oil heat exchanger are placed in the cover. Since the single opening is shared by the two heat exchangers, rigidity deterioration of the cylinder block due to making an opening is suppressed to the minimum. This also contributes to vibration reduction.
The oil heat exchanger may include a plurality of thin plate-like hollow members immersed in the engine cooling water in the housing, and the EGR gas heat exchanger may likewise include a plurality of thin plate-like hollow members immersed in the engine cooling water in the housing. The cooling system may include a first passage for introducing an exhaust gas to the EGR gas heat exchanger from an exhaust manifold and a second passage for introducing the exhaust gas to an intake manifold from the EGR gas heat exchanger. The housing may be shaped to guide air generated upon heating of the engine cooling water in the housing to a water jacket thereby allowing the air to escape to a cylinder head Therefore, the air ventilation pipe required in the conventional EGR cooler shown in FIG. 8 is unnecessary for the cooling system of the invention.
Additional objects, benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the embodiments and the appended claims, taken in conjunction with the accompanying drawings.